1. Field of the Invention
The present invention relates to a thin film magnetic head for use in head disk assemblies (HDAs) such as magnetic disk apparatuses, and more particularly to a thin film magnetic head compatible with high recording density, excelling in recording performance, and a method for manufacturing the same.
2. Description of the Prior Art
In recent years, along with the capacity enlargement of computers, the requirement for higher recording density of magnetic disk apparatuses is increasing more and more. In this connection, an ever narrower width is required for thin film magnetic heads to be mounted on magnetic disk apparatuses, as the width determines the track width of magnetic cores mounted thereon, and the requirement for their manufacturing accuracy is becoming increasingly stringent. Furthermore, the recording performance is also required to be high enough to prevent blurred recording of signals onto the magnetic disk and to ensure a high output stably.
FIG. 2 is a section of the essential part of a thin film magnetic head according to the prior art whose coil is structured in a single layer, and FIG. 3 is a perspective view of the same. As shown in FIG. 2, the air bearing surface of the magnetic head is supposed to be at the left end of the magnetic head as viewed in the drawing. In the following description, the upward direction in FIG. 3 means the upward direction in the magnetic head; the downward direction in FIG. 3, the downward direction in the magnetic head; the direction corresponding to that of the air bearing surface of the magnetic head shown in FIG. 2, the direction of the air bearing surface; and the direction of the width determining the track width of the magnetic recording medium, the track width direction. These definitions apply not only to FIG. 2 or FIG. 3 but also to all other sectional views or perspective views cited in this specification.
To add, FIG. 2, FIG. 3 and all other sectional views or perspective views appended to the present application show only the essential part of the magnetic head on its air bearing surface side, but no illustration is made of the portions of the magnetic head in the direction reverse to that of the air bearing surface or in the downward direction of the magnetic head. However, it goes without said that the unillustrated portions are compatible with all kinds of magnetic heads.
As shown in FIG. 2, the thin film magnetic head is configured of a read head section and a write head section successively formed of a substrate 11 consisting of alumina-based ceramics.
The read head is formed of insulating film, a lower shield film 111, a magnetoresistive film 10 and an upper shield film 112, all formed over the substrate 11. As the magnetoresistive film 10, one of various kinds of elements that are sensitive to a magnetic field and can take out a read output, such as an AMR element, a GMR element or a TMR element, can be used.
The write head is separated from the read head by an insulating film, and is configured of a lower magnetic film 12 formed to be coated with a magnetic film, a magnetic gap film 14 which is a non-magnetic film of a metallic oxide, such as SiO2 or Al2O3, formed over the lower magnetic film 12, a first insulating layer 13, a conductor coil layer 15, both formed over the magnetic gap film 14, a second insulating layer 16 formed over these layers, and an upper magnetic film 17 formed over the magnetic gap film 14 and the second insulating layer 16 and constituting, together with the lower magnetic film 12, a magnetic core which forms a magnetic circuit.
This configuration results in the formation, at the tip of a track, a magnetic gap between the upper magnetic film 17 and the lower magnetic film 12. Incidentally, the conductor coil layer 15 passes between the upper magnetic film 17 and the lower magnetic film 12 and crosses the magnetic circuit. In the write element portion of the thin film magnetic head so far described, the upper magnetic film 17, the lower magnetic film 12 and the magnetic gap (the magnetic gap film 14) at the tip of the track constitute the air bearing surface portion of a thin film head slider, and writes information onto a magnetic disk (not shown).
The recording density of such a thin film magnetic head according to the prior art is determined mainly by the shape of the upper magnetic film. The particularly important factors of the shape include the width of the upper magnetic film 17 which determines the track width, the pole length (the thicknesses of the lower magnetic film 12 and the upper magnetic film 17) which determines write capabilities including overwriting capability, the thickness of the magnetic gap which determines the resolution, and the position of the throat height=0. All these factors should be formed with high precision.
Of these factors, forming the width of the upper magnetic film 17 which determines the track width requires accurate formation of a pattern of a portion of the lower magnetic film 12, which is positioned close to the lower part of a level gap formed of an insulating film of about 10 μm in height (the portion where the first insulating layer 13, the conductor layer 15 and the second insulating layer 16 where they are stacked in full height) and a portion of the upper magnetic film 17 opposite the lower magnetic film 12 with the gap film 14 in-between. These two magnetic films are formed by a method known as pattern plating or frame plating, usually employing a photoresist pattern for masking. The photoresist pattern should preferably be thin in film thickness in order to keep the width which determines the track width narrow and to form a highly accurate pattern.
In forming the pattern, the resolution which is the limit value of width formation to determine the track width is represented by k·λ/NA, where k is a coefficient, λ is the wavelength of the light to which the pattern is exposed and NA is the numerical aperture of the lens. The focal depth, which is the reference for the region coming into focus in pattern formation, is represented by k·λ/(NA)2. These relations indicate that, in order to make the resolution fine, it is required either to shorten the exposure wavelength or to enlarge the numerical aperture NA of the lens. This, however, would make the focal depth shallow, namely narrow the region in focus at the time of pattern formation, and therefore the pattern would not be resolved sufficiently unless the resist film thickness is thin. In other words, the thinner the resist film thickness, the shorter the exposure wavelength or the smaller the numerical aperture NA of the lens can be. Thus it is thereby made possible to make the resolution finer, narrow the width that determines the track width and achieve highly accurate formation.
Where the photoresist pattern is to be applied to a portion of a high level gap formed by the second insulating layer 16 as shown in FIG. 2, the characteristic of the application is such that the photoresist pattern tends to be formed thicker toward the bottom of the gap, in a thickness of 10 μm for instance. This greater thickness of the photoresist in the position where the width to determine the track width is to be formed makes too thick relative to the required plating thickness of the magnetic film and thereby makes it correspondingly more difficult to form a highly accurate pattern.
There is also adopted a method by which, as shown in FIG. 3, the blurring that occurs when writing signals onto a disk is minimized to achieve high density magnetic recording by making identical the widths of the upper magnetic film 17 and the lower magnetic film 12, opposite each other with the gap film in-between, in the track width.
Furthermore with a view to forming the width to determine the track width with high precision, studies are being made on a method to form with high precision the width of the upper magnetic film 17 in the position of the air bearing surface in a state in which the level gap of the insulating film is low, i.e. the width in the direction of the write track width for the purpose of forming a highly precise photoresist pattern by thinning the thickness of the applied photoresist to the necessary minimum.
For instance, the Japanese Patent Application Laid-open No. 2002-8209 discloses a magnetic head whose upper magnetic film is configured of an upper first magnetic film constituting the upper pole and an upper second magnetic film to function as the upper yoke. The thickness of the photoresist is reduced to about 4 microns, making it possible to form a pattern whose width to determine the track width can be as small as about 0.3 micron.
A section of a magnetic head according to the prior art, whose upper magnetic film is configured of two magnetic films, is shown in FIG. 12. After forming a first insulating layer 18, only the tip portion 182 of the upper magnetic film is formed and, after forming a protective film 19 for the tip portion, an insulating film 20 and the rear portion 183 of the upper magnetic film are formed. This method has a feature that, as the track width is determined by the width of the tip portion 182 of the upper magnetic film in the direction of the track width, the width of the upper magnetic film in the direction of the track width can be formed highly accurate in a state of a low level gap in which only the first insulating film 18 is formed. Moreover, since the protective film is provided over the magnetic film which constitutes the track, no variation in pole length occurs from processing in the subsequent manufacturing process, according to the patent application.
The prior art stated in the Japanese Patent Application Laid-open No. 2002-8209 takes no account of a method of forming the width, as narrow as no more than 0.3 micron, which determines the track width. In order to realize a width as narrow as 0.3 micron or less, it will be necessary to further reduce the thickness of the photoresist or to take some other measure.
Further it is desirable to make flat the surface of what is formed first of the two split potions of the upper magnetic film, and this is done by polishing the surface flat by a CMP technique or etching back, for instance after embedding the insulating film. This makes it necessary to take into consideration fluctuations of the quantity of polishing by CMP or any other method as tolerance, and accordingly prohibits a sufficient reduction in the film thickness of the photoresist.
This problem will be discussed in more specific terms with reference to FIGS. 13A to 13G. FIGS. 13A to 13G are diagrams showing how the tip portion of the upper magnetic film of the magnetic head of the structure shown in FIG. 12, for instance, is formed as viewed from the air bearing surface.
First, as shown in FIG. 13A, after the lower magnetic film 12 and the magnetic gap film 14 are formed, the photoresist 181 is formed so that the width of the tip portion 182 of the upper magnetic film in the direction of the track width determine the track width.
Then, as shown in FIG. 13B, the tip portion 182 of the upper magnetic film is formed using the photoresist 181. After that, as shown in FIG. 13C, the photoresist 181 is removed and, for dimensional adjustment of the tip portion 182 of the upper magnetic film, a part each of the lower magnetic film 12, the magnetic gap film 14 and the tip portion 182 of the upper magnetic film is removed as shown in FIG. 13D. After the dimensional adjustment, the insulating film 19 is formed as shown in FIG. 13E.
Next, as shown in FIG. 13F and FIG. 13G, the tip portion 182 of the upper magnetic film and the insulating film 19 is flattened by CMP, etching back or otherwise. Here, it is necessary to form the tip portion 182 of the upper magnetic film thicker than the required minimum film thickness in advance to allow for the tolerance of fluctuations in the machining of the flat surface in the flattening process. Correspondingly, the photoresist 181 should also be made thicker.